UK scientists seek silent aircraft

Today saw the launch of an ambitious £2.5m, three-year project led by Cambridge-MIT Institute (CMI) - the Silent Aircraft Initiative (SAI). Its plan is pretty simple: to produce aircraft "whose noise emissions would barely be heard above the background noise level in a typical built-up area".

The initiative boasts an impressive manifest of partners, including British Airways, the Civil Aviation Authority and Rolls-Royce. It also aims to consult representatives of community groups opposed to aircraft noise - a sensible move given the current brouhaha over the proposed extension to London's Stanstead Airport and ongoing protests surrounding increased air traffic at Heathrow.

According to Cambridge SAI professor Ann Dowling - quoted on the SAI website - "The civil aviation industry is already introducing small, incremental decreases in aircraft noise. But we are aiming for a radical change in noise levels - so that beyond the perimeter of the airport, the noise of aircraft flying would be imperceptible to the public."

All well and good, but how? We asked project manager Paul Collins if the research would centre on existing jet turbine technology, or would it embrace newer, more radical solutions? He confirmed its radical nature, but noted that "it still flies and carries passengers and yes, it's still powered by gas turbines".

This is an interesting line of attack, and one completely different to that adopted by NASA and its scramjet-powered Hyper-X programme, which the agency hopes will eventually promise "to increase payload capacities and reduce costs for future air and space vehicles". It's also a big leap from other current gas turbine-driven developments. The Boeing 7E7's main techie selling point is its composite materials body and wings. Its principal commercial appeal lies in a quoted 20 per cent fuel saving over other equivalent aircraft.

Airbus's A380, in contrast, is going for the "more is more" approach, packing 555 paying punters into two decks. However, both the A380 and 7E7 are simply technologically-advanced offspring of a tried-and-trusted design concept.

SAI is approaching the commercial airliner from another tack - its fundamental consideration being noise rather then necessarily capacity or pure fuel economy. Tackling this key issue centres around "making the aircraft as slippery as possible," according to Collins. This points to a blended wing concept, with the engines incorporated into the aircraft's structure. Collins explained that, for example, an aircraft coming into land at 600mph has to dissipate a lot of energy - around eight megawatts - and extruding structures such as engines and undercarriage generate a hell of a racket.

The design is just part of the plan. Collins spoke of "new operational procedures" which might contribute to an overall noise level reduction. MIT in the US is already investigating how alterations to an airliner's glide path into an airport might have a beneficial effect on the ears of those below.

In the end, though, the proposal must "buy itself into the airlines". There's little point developing a stealthy passenger-carrier if the operators won't touch it, as Collins acknowledges. In short, it has to fit in with the existing infrastructure.

And as for Mother Earth, Collins is adamant that any future airline innovations must address environmental considerations: "The effects [of jet engines] on the environment are not fully understood. We are planning outreach activity to raise the profile of the debate so that people become more aware of what the issues are."

An overview of the SAI is available here. Collins asked us to note that the website is currently awaiting expansion to cover all aspects of the various teams' research. ®